During the completion of petroleum related wells several lengths of casing are run into the well while it is filled with mud or well produced fluids. While the rather long strings of pipe are moving into the well, the fluids fill the newly lowered pipe.
If casing or liner pipe strings are moving axially along the well bore the resulting pressure differentials along the bore can be destructive. The casing acts as a pump plunger and may be driven by several hundred tons of steel pipe. Serious formation damage can result. To prevent formation damage, the pipe string is moved slowly to allow fluid to flow around and through the pipe string to reduce the pressure effects. Moving slowly takes more time for well completion and time is costly and may well invite hazards to property and personnel.
When the formation damage risk is avoided, there are other problems that arise from moving pipe into wells. There is some flow resistance and the fluid is still flowing into the moving pipe when the top end of the pipe string is stopped just above the rig floor to add a new pipe section to the string. Flowing fluid, in a long pipe, is not easily stopped and it flows out the top of the pipe, usually before downward movement of the string is completed. The well fluid flows over personnel, rig machinery, and rig floor. The fluid adds to personnel risks, is slippery, and generally unpleasant.
Casing or liner that does not extend to the surface when installed is put in place by a working string that is, finally, disconnected from the placed installation string. The working and installation strings are connected by an adapter. The working string has a small bore compared with the flow area of the annulus between the working string and the well bore. The flow area of the annulus is needed to reduce surge pressure below the installation string. Fluids below the casing are less likely to build up destructive pressure that damages formation, or flow over the top end of the working string if they can be vented into the well annulus above the pipe string being installed.
The adapters have been constructed such that the upwardly moving fluid can flow in both the annulus and the pipe string bore. Further adaptation has made it possible to pump fluid down the string without losing it to the annulus at the adapter. When installing pipe strings in wells it is often necessary to circulate to ease past tight spots and to blow out bridges.
To date, maximizing protection of the formation, and optimizing installation speed has not eliminated the overflow of fluid at the top of the working string. The prospect of using a flow resistor in the working string bore is discouraged because a wide open pipe bore is needed for some well completing operations, including the running of cement. There is a need to provide means to allow free flow downwardly in the working string, but to restrict upwardly moving fluid so that the annulus fluid level, drained at the surface, will be above the level of fluid rising in the bore of the working string. Then, fluid will not flow over the top of the working string.